This invention relates to a finder display for a single lens reflex camera wherein a shutter speed (Tv) scale and a diaphragm or aperture value (Av) scale are disposed side-by-side, and either one may be selectively illuminated.
As is well known, automatic exposure control systems in SLR cameras are generally of either the diaphragm priority (EE) type or the shutter speed priority (ES) type, and it is customary that the former displays the Av indication in the finder while the latter displays the Tv indication. Which type of indication is best suited for an automatic exposure control system cannot be stated previously as it is largely dependent upon the conditions of the photographic object and the photographer's intentions. A demand thus exists for a camera wherein the exposure control system can be changed over from the ES mode to the EE mode, and vice versa.
It is necessary for such a camera to display either the Tv indication or the Av indication in the finder, corresponding to the ES control mode or the EE control mode, and for implementing this function various types of electro-optical elements have been used. Prior to describing the present invention, several known display devices utilizing a light-transmissive type of liquid crystal cell will first be mentioned.
Referring to FIG. 1, a liquid crystal cell 1 bears a Tv scale 2 for the ES mode and an Av scale 3 for EE mode, each containing numerical graduations as shown in FIGS. 2 and 3. Reference numerals 4 and 4' designate LED indicators or the like for representing the Tv or Av ouputs of the exposure meter circuit, and 5 is the finder viewing field. Such an arrangement, wherein the Tv and Av scales are independent and each has its own indicator 4, 4', suffers from the drawbacks that: (1) the liquid crystal cell is unduly large; (2) it occupies too much of the finder viewing field area; and (3) the use of two indicators increases the number of terminals to be connected to a drive circuit.
Referring to the alternate arrangement shown in FIG. 4, a liquid crystal cell 6 containing a Tv scale 7 and a dot indicator 8 is disposed on the right side of the finder field, and a liquid crystal cell 9 containing an Av scale 10 and dot indicator 11 is disposed on the left side. With this device, however: (1) the area of the finder field is decreased, and since the two indicator cells are provided on opposite sides, handling difficulty results; and (2) the space for attaching the two cells as well as the space for their wiring is increased, thus requiring a larger and more costly camera body. The Tv and Av scales could be disposed in series as shown in FIG. 5, but this is impractical because the indicator numerals must be made to small for convenient use.